The term "Orthodoxy" is applied to Jewish traditionalist movements that have consciously resisted the influences of modernization that arose in response to the European Emancipation and Enlightenment movements. It is not usually employed to designate Jewish traditionalism prior to the modern era, nor does the phenomenon appear in communities that were unaffected by the Reform movement; e.g., in North Africa, or in Eastern Europe before the mid-nineteenth-century.

The adjective "Orthodox" ("correct belief") is taken from the conceptual world of Christianity, where it denotes a conservative and ritualistic religious outlook, as viewed from the perspective of liberal Protestantism. It appears to have been first applied derisively to Jewish conservatives by a Reform polemicist in an article published in 1795.

...it was not "Orthodox" Jews who introduced the word "orthodox" into Jewish discussion. It was the modern "progressive" Jews who first applied the name to "old," "backward" Jews as a derogatory term. This name was at first resented by "old" Jews. And rightfully so...

Yet so pervasive was the use of the term that in 1886, when Hirsch established an alliance of the traditionalist congregations in Europe, he named it the "Freie Vereinigung für die Interessen des Orthodoxen Judentums" (Free Union for the Interests of Orthodox Judaism)!

Of all the movements on the contemporary Jewish scene, Orthodoxy is the least centralized and the most diverse. Whereas the Conservative and Reform movements in America each has a single seminary, Rabbinical association and synagogue union, the Orthodox world is fragmented into diverse institutional structures. Though they agree on basic issues of religious authority (e.g., the divine origins of the Bible and Oral Tradition) and the commitment to the study and observance of Jewish law, the halakhah as interpreted in a relatively inflexable manner, Orthodox Jews diverge on a broad range of secondary issues, such as: